Concentrated formaldehyde solution



July 26, 1960 B. o. KRUEGER ET AL 2,946,403

CONCENTRATED FORMALDEHYDE SOLUTION Filed Aug. 15, 1958 DEPHLEGMATOR T VENT GASES wan/ 24 T0 SCRUBBER "and? J u 22 WATER J,

29 T METHANQL METHANOL TAKE-OFF h SURGE X28 fZZIIILuIn REFLUX ALKALI CONTROL 3o 32 :5" 5 DRY 46 i; UREA 5:::::' LEVEL 1 FEED AH 42 CONTROL I M 48 a, 'r FORMALDEHYDE T 38 i 36 CONVERTER meauA g unaA \COLUMN PUMP 34 STEAM 5o REBOILER CONDENSATE PRODUCT WITHDRAWAL INVENTORS BRUNO o. KRUEGER BENJAMIN a. BUTLER JOHN M. HINE ROBERT CALVERT ATTORNEY ilnited 1 States 2,946,403 CON CENTRATED FORMALDEHY DE SOLUTION Bruno Otto Krueger, Benjamin B. Butler, and John M.

Hine, Seattle, Wash, assignors to The Borden Company, New York, N.Y., a corporation of New Jersey Filed Aug. 13, 1958, Ser. No. 754,858 8 Claims. (Cl. 183 1'15) in a representative run in which the formaldehyde was used' in the form of furnace gas from methanol conver sion containing 30.5% of formaldehyde, the recovery was atent complete to within the accuracy of the weighings and '1 analyses. Of this total, 95% of the formaldehyde appeared in the form of a solution containing 83.5% by wvelght of urea and formaldehyde, with a formaldehyde content or" 55.6% in the form of such combination with urea that the formaldehyde did not separate, as paraformaldehyde or otherwise, on cooling the solution to the lowest winter temperatures. tion may be shipped with a water content of only about l6%l7%, with attendant saving in transportation cost over that for the less concentrated solutions of commerce, and then mixed with additional urea at the place of use in making urea-formaldehyde resins.

Briefly stated the invention comprises the absorption of gaseous formaldehyde by passing the formaldehyde upwardly and in intimate contact with a descending solution of urea, melamine, or the like, the solvent therefor consisting principally of water in the lower part of the column and, in the upper part of the column, largely of a C -C alcohol or a Water soluble organic liquid that is a better solvent for formaldehyde and a poorer solvent for urea than water is. In the commercial embodiment, the invention comprises passing the formaldehyde gas upwardly through a heated fractionating column in counter current relationship to a solution of urea in an alcohol or mixed water and an alcohol. Vapor of the selected alcohol rises to a reflux so that the upper part of the column contains a higher concentration of the said alcohol than does the lower part of the column. A concentrated solution of the formaldehyde in the aqueous urea acceptor solution is withdrawn from the bottom of the column. Y

The invention will be illustrated in connection with the attached drawing to which reference is made. .Parts The concentrated soluice amount of the solution through line 42 as a reflux to the column. This reflux enters the column at positions 4 42-, 46, and 48, all of which are either at the top of the column or between the top and the middle thereof, and in all cases above the level at which the formaldehyde gas is introduced into the column. Line 50 delivers material from the bottom of the column to the reboiler equipped with usual steam heating c'oils (or shell) provided with vapor outlet 54 by which vaporized formaldehyde andorganic solvent, if any remain, arereturned to the-column near the bottom thereof, along with some steam.

T he operation ofthe equipment will be further illustrated in connection with the use of-formaldehyde gas direct from a converter (sometimes called burner -or furnacelin which methanol is converted to formaldehyde by oxidation, dehydrogenation, or both and the organic solvent used is methanol. The fractionating column in thiscase is packed with ceramic saddles or rings such as commonly used in packed fractionating towers. The

column of liquid that moves downwardly over the pack-I ing is not a continuous mass of liquid but a series of liquid films wetting the tower packing. Methanol and 7 urea are charged to the mixing tank 34 in proportion to provide 300 grams of the urea for 3000 ml. of the resulting solution. The pump is then started and the said solution is delivered through line 42 to a position near the top of the fractionating column, at such a rate as to wet the surfaces of the saddles in the column and keep them'continuously wet with the urea solution.

The formaldehyde converter gas is introduced through line ii-2 and the introduction of the methanol urea solution and the formaldehyde gas is made continuously, at such rates as to provide about the proportions in which the formaldehyde and urea are to appear in the final product delivered through line 53. The effluent from the bottom.

of the column into the reboiler is there subjected to steam heating sufiicient to distil therefrom substantially all methanol reaching the reboiler and also some of the reof the apparatus that are not shownin detail are con- Y ventional.

There are shown fractionating column 10, a connection such as pipe 12 for delivering a gaseous mixture ,containing formaldehyde to the column at a position 14 near the bottom'or at other. positions 16' and 18 between the bottom and approximately the middle of the column,

7 the vapor line 20 delivering vapors to the dephlegmator 22 with vent 24 leading to conventional scrubber, equipment (not shown), and outlet 26 delivering condensed liquid to a surgetank 28 for such liquid with draw-01f line 30 tovalve. 32 from which the liquid condensate passes to a mixing tank 34 into which dry urea is supplied at maining, volati-lizable formaldehyde, and a part of the water present, these materials being re-used, as by being returned through line 54 to the column and acting with the hot furnace gas to heat'the liquid at the lower end of the column to a temperature above the boiling 'point of methanol. 'As a result the methanol vapors rise through the column. The methanol becomes concentrated in the upper part thereof, absorbs formaldehyde there available, and passes in part through the dephlegmator from which both are returned eventually by pump 4%) to provide the solvent for the urea and also reflux at the top of the fractionating column.

The alcoholic urea solution, on'the other hand, works downward in the column, counter current to the ascending stream of gas in which the'formaldehyde is originally introduced; On its Way downward, the alcoholic urea solution leaves the methanol zone at or near the top of the column, with steady absorption of formaldehyde, and-enters the water rich, higher temperature zone towards the bottom. The water there is essentially a condensate. from the converter 'gas or is added with the alcoholic urea solution in case a' less concentrated product is to be made and Withdrawn from the line 53. Constantly increasing temperatures downwardly in the column '1' The urea,

together With-the absorbed formaldehyde, changes-over cause gradual evaporation of the methanol.

into an aqueous solution.

The solubility of urea in water at approximately 20 C. is 108 g. for of water. The solubility in methanol at 30 C. is only about 28 g. The solubility of urea in other C -C alcohols is much lower than in methanol.

As methanol recovered from the system builds up' to an amount more than required, the surplus methanol may parts. 7

l be drawn oii from the methanol take-oif line 29. This build-up of methanol is due to the unconverted methanol content of the furnace gases supplied through line 12.

This methanol so drawn ofi may v contain some forrn aldehydeand may be iised to advantage -in the conve sioriip lantin which the methahol is Qxidized and r t d l f m s dhifiekt r ssess-nears "8 it liner As j o materials used, thetor naldehyde may he that stillati from commercial s yi l iwt sl a. a.

commercial aqueous soluparaforrnald hyde orfrom tion ot. formaldehyde} we; hairs 'vers fsa 's w y ti.

6 q snis. sh eat lt fo imse i ti n. o t-th 0 1 Y tion of sweat?! an, pra sq e t et tim ehyde? PatP 0f th ts mn lw in the ph eeust be one that is soluble in water or at least pif. ls e e' n'f's t at. the may h e ss to the rea'in thesaid solvent and extract theurea there- It must be one that is lower in boiling point ate'n ie. distillable from watcr in a mixture containingsmore of the organie solvent in the vapor phase ao W tery. a ple of m eria t t these I q fimn ss ith m y b n dsa methanol,-v e han psq aao nn-rr pan a dfiuta l bt in p r. ticularly satisfactory.,r esults when theaalcohol used is methanol,

The oiganie liquid sclected should be a better solvent thantyvaterufor formaldehyde, that is,. should dissolve 1 thejormaldehydefaster than water, show higher retention,- or both.. The -reten'tivity decreases removal of forms aldehyde; .by. residual gases passing. through the solution.

This retentivity foriormaldehyde is considered to bedue in part-to the formationoi a hemiformal,

To; decompose the; methanol-formaldehyde, combination (presumably in part a formal),.so that the-two components,-,rnay be separatedby distillation, we maintainf a reboilertemperature between, 100 and, 120? C.

When the formaldehyde is supplied in the form of gases fromthe ifurnacespr methanol converters, the gases will contain a'small proportion. of'formicacid If it is desirablelo neutralize lthis forrnic.acidthere maybe used an alkali. This; alkali is ordinarily: a watervsoluble alkali metal-hydroxide ;or;carb onate,ot amine such'as triethanol-r. amine.:-..lt is introduced'into.3thesystem at anyconven ient position, as throughathezline :35;

5 As to proportions, :thetiurea (may bevariedas between t '30-.60.=parts' for: 1001'of the 'formaldehyderepresental cally stated'to'thepontraryq t d. the desired level, as for instance within the range 8-12 at the top of column 10, that is, at the upper level of the urea and alcohol solution introduced as shown. Ordinarily We add the alkali in amount to adjust the pH at this position to 10-11.

As to conditions of operation the gases, when from the methanol converter, are -introduced at a temperature above he d l a-P le; 9 FiQQe3 i h?QlIl-r? a ahaut; 120f 4 0 0 C. and ormally about 13( )-275 C., through inlets 14;:16,M182 i e-eme e: tq eth f l a id t s l t is aini tained"below"'the bdilingp'o'iritbf 'w'ater"exce at 'posi tions adjacentgto the introduction .eof :;t he, hot furnace gases. In a typical run, ,t he ponverter gases came in at the point 18, the heightofcolumnused'was 4 feet and inside diameter approximately 1.5 inches, the tower packing was 6 mm. ceramic berl saddles, the column efiiiiYeQPEFQWQEQlY: flWlsYQlQQHQ r Q. theoretical fllla'y tl ets s atuse ifiadltlgs in h gfi l nlttsliquid were;

1 at ar n lthep sk n @JZQYE mediums... 9444s s -renam 3 t st 112 at fi mr,

Infgeneralthetemperature'at'thelower'exit end of the'woluinnis kept-below the boilingpoint "of water but above-the--boiling point of theforganic"solvent.' The temperature -atthehead' of fthe"co'lumn jis maintained at approximatelyythe refluxing pointpfthe organic sol'- "I'he rate of flow of the liquid through'the reboilerf and-the supply"'of"heat' tothe reboilef'areso adjusted thatsome'ofthefremainingfvolati'leformaldehyde as well as =any '0rganic' solventpresentfiarddistilld from the 1 liquid-in the reboiler andreturned"toithecolurnnthrough the line 54.

The invention will 'befurther" illustrated by description in connection"with*thei'specific'examples of thepra'ctice of it In' these'"examples KandeISeWherejherein all pro-1 portions are expressed as 'partsfby' weight -unless specifi- EXAMPLE- 1 A solution-of. 300 p. ofureain 2,260 *of pure meth-' anol- I was prepared, the total volume being 3,000 r ml.

The rpH was adjusted to --10'-;to-11-'by the addition-0f sodium hydroxi'de selutiorri This solutiorr was then fed a to thetop of a 4-ft5 x 1.5 in. packed absorption distillation towers-through a flow-meter at' a'rate'of 8;.33"ml. per minute as reflux:

Furnace gas-=from the" conversion of methanol to formaldehyde 'was introduced through inlet 18 and'its" taneouslywith the introduction ofthe'reflux solution at the top of the tower.

AbOut -ZO miriutes aftePthe StaIt; sufficient liquid had accumulatedin the reboiler-to -permit its-operation; The;

from the condensen: 221 A prog'ressively lower soneen- 7 tratioir oi methanol in -the reboile'r made room for fur'..

tive-tzratiotin thefinished stahlensolution is 1 mole -.of-'-- urea'to 4 of formaldehyde. ...Melarnine nsedaisalso It'll-60,

Waterrisintroduced as it"occurs in the gas :-in whitah the-cformaldehydei -i'ssupplied or is added separately b make a total of about 2065'-parts for 1 0O of the' real used iandz' 10 -:30' for 100 of the' conc entrat'ed solutions constituting the .zfinished product. 1

The alkali is Y addedtin amount ;to establish= the pl-l at thet down coming. produet un-til' the' desired temperature in the reboiler"liquid-indicated the -lowest possible meth-'-- anGl -O1iC6l1imtl0Ii I Thesreb'oiler: liquid: temperature was ythen kept com stant"at -1 1 l -T.1- 1 1 f -andthe-'level o'f th'e liquidtherein? maintained by co'nti 'nuous produet withdrawal;

Periodioodorchecks'i-wer'emade on-the tailgasescaping"thr'oug'lt vent fM. Only methanol'couldbewdetecmd whih indicatedfno sub'stantial lossof formaldehyd'es The methanol condensate iron-1 the :COHdQ'lSeF was 'colmateria'l balance calculations.-

lected in I a graduated cylinderand lat'ee 'analyzed for-*- 1 aeaeaoe The total run was 6 hours. The product withdrawn through line 53 was cloudy to hazy at first and later clear.

ANALYTICAL RESULTS AND MATERIALS PRODUCT WITHDRAWN FROM REBO ILER Grams in 6 hours Formaldehyde 597.9 Urea 300.3

Methanol 8.6

Water 167.1

Total 1073.9

MATERIALS BALANCE (INERTS NEGLECTED) Formal- Methanol Water Urea dehyde Furnace gas, condensables 630.1 713.9 401. 4 Methanol-urea solution 0 2, 260. 0 0 300. 0

Total supplied 630.1 2, 973. 9 401.4 300 O Recovered in product from reboiler. 598. 0 8. 6 167. 1 300.0

Remainder 32. l 2, 3 234. 8 0 Recovered with methanol.. 32. 1 2, (E83. 204. 4 0 In tailgas to scrubbers, by difference 0 281.8 29. 9 0

CALCUIJATED ANALYSIS FOR AVERAGE. PRODUCT (FROM MATERIALS BALANCE) The procedure and proportions of Example 1 were followed except that the operation was performed on a commercial scale, the formaldehyde-containing furnace gas was introduced at l35l75 C., and the methanol recovered from the condenser (here the dephlegmator 22) was mixed with additional urea and with sodium hydroxide in the mixing tank 34 and returned as reflux to the top of the fractionating column. As methanol built up in the system, due to the methanol content of the formaldehyde converter gas fed through line 12, the surplus methanol was withdrawn through the methanol take-off line 29. The reboiler temperature was varied between 106 C. and 118 C.

EXAMPLE 3 The procedure and compositions of either Example 1 or 2 are used with the exception that the methanol there used is replaced by an equal weight of any one of the other alcohols shown herein and the overhead column temperature was maintained at the boiling point of the selected alcohol or somewhat higher.

EXAMPLE 4 The procedure and composition of any of the Examples 1-3 are used except that the formaldehyde converter gas supplied through line 12 is replaced by formaldehyde obtained by distilling formaldehyde from a commercial aqueous solution of formaldehyde such as one containing 37%44% of actual formaldehyde.

EXAMPLE 5 The procedure and composition of Example 1 are used except that the urea there used is replaced by an equal weight of melamine.

The process described is economical. It gives in a single step and continuously eflicient absorption of the formaldehyde, recovery and rectification of the methanol content of the converter gas, and a concentration of the formaldehyde-urea product up to 85% or so without a subsequent concentrating step.

The concentrated solution so made is useful as an intermediate product in the manufacture of urea-formaldehyde resins suitably after the addition of a further proportion of urea (or melamine if used originally) in amount to establish the ratio to formaldehyde desired in the finished aminoplast resin and also after the addition of any usual catalyst of condensation with formaldehyde.

The concentrated solutions made as described are ad vantageous in transportation by reducing the proportion of water to formaldehyde much below that previously used and in avoiding the separation of paraformaldehyde at low temperatures, as down to 20 C. or somewhat lower.

It is to be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

We claim:

1. In the absorption of formaldehyde, the process which comprises passing formaldehyde in gaseous form upwardly through and in intimate contact with a solution of a formaldehyde acceptor selected from the group consisting of urea and melamine and dissolved in a water-alcohol medium, the alcohol being water soluble and of boiling point lower than water and the said solution descending in a column under fractionating conditions countercurrent to the upwardly rising formaldehyde, maintaining the proportion of the selected alcohol higher than that of the water in the upper part of the column and below that of the water in the lower part of the column, heating the said column at a lower part thereof and maintaining the said medium at the top of the column at about the temperature of refluxing for the said alcohol and at the bottom of the column at a point between the said temperature and the boiling point of the water in the solution at that level, continuing the passing of the formaldehyde through the acceptor solution and the said heating so that a concentrated formaldehyde-acceptor solution resulting from the action of the formaldehyde on the acceptor collects in the lower part of the column and the alcohol becomes concentrated in the upper part of the column, withdrawing the concentrated solution from the said lower part and the alcohol in vapor form from the upper part of the column, and supplying to the said column additional amounts of the acceptor as required for accepting the formaldehyde, the acceptor being introduced at a position above that of introduction of the gaseous formaldehyde.

2. The process of claim 1 in which the said acceptor is urea.

3. The process of claim 2 in which the said alcohol is methanol, the formaldehyde, methanol and water for i the acceptor liquid are introduced into the said solution in part at least in the form of mixed gases and vapors from methanol conversion to formaldehyde, and the temperature of the said mixed gases and vapors is about 400 C.

4. The process of claim 1 in which the formaldehyde is introduced predominantly in the monomeric unhydrated form and the said alcohol is methanol.

5. The process of claim 4 in which the said acceptor is urea, the formaldehyde and methanol are introduced into the said solution of a formaldehyde acceptor in the form of the mixed gases and vapors from methanol conversion to formaldehyde, the temperature of the mixed gases and vapors is about 120-400 C and a water toluble alkali is introduced into the said eolurnh at a position above that of introduction of the said nrixed gases and vapors and in amount to establish the pH at abouLS-IQ; w M v W I d I 6. The process of claim 1 which includes heating the withdrawn eorrcentrated formaldehyde-acceptor solutionjo distil therefrom any rmaining valcohol. I

7. The process of claim '1 which includes condensing the said alcohol withdrawn in vapor form and introducing the said additional amounts of the acceptor ear.

the top of the column and in solution in a part at-least of thealcohol after the said condensing thereof.

8. The 15rocess of claim 1*in which thesaid alcohol 15 is methanol, the'formaldehyde aceeptor' is urea, the formaldehyde' 'and methanol are introduced-Etc the sdlutidh of the urea in the form of the mixed gases and vapors from=methanol conversion to formaldehyde, 'aud sodium hydroxide is introduced into thesaid column at a position above that of introduction of the formaldehyde and metha'fio1itit'o"the solution "bf urea and in' amount to' 'establish the pH at about-842.

7 References Cited in the file of this vfiatent UNITED STATES PATENTS *Reneeret 515 i a n, *1'94'1 KiSG'a-u 

1. IN THE ABSORPTION OF FORMALDEHYDE, THE PROCESS WHICH COMPRISES PASSING FORMALDEHYDE IN GASEOUS FORM UPWARDLY THROUGH AND IN INTIMATE CONTACT WITH A SOLUTION OF A FORMALDEHYDE ACCEPTOR SELECTED FROM THE GROUP CONSISTING OF UREA AND MELAMINE AND DISSOLVED IN A WATER-ALCOHOL MEDIUM, THE ALCOHOL BEING WATER SOLUBLE AND OF BOILING POINT LOWER THAN WATER AND THE SAID SOLUTION DESCENDING IN A COLUMN UNDER FRACTIONATING CONDITIONS COUNTERCURRENT TO THE UPWARDLY RISING FORMALDEHYDE, MAINTAINING THE PROPORTION OF THE SELECTED ALCOHOL HIGHER THAN THAT OF THE WATER IN THE UPPER PART OF THE COLUMN AND BELOW THAT OF THE WATER IN THE LOWER PART OF THE COLUMN, HEATING THE SAID COLUMN AT A LOWER PART THEREOF AND MAINTAINING THE SAID MEDIUM AT THE TOP OF THE COLUMN AT ABOUT THE TEMPERATURE OF REFLUXING FOR THE SAID ALCOHOL AND AT THE BOTTOM OF THE COLUMN AT A POINT BETWEEN THE SAID TEMPERATURE AND THE BOILING POINT OF THE WATER IN THE SOLUTION AT THAT LEVEL, CONTINUING THE PASSING OF THE FORMALDEHYDE THROUGH THE ACCEPTOR SOLUTION AND THE SAID HEATING SO THAT A CONCENTRATED FORMALDEHYDE-ACCEPTOR SOLUTION RESULTING FROM THE ACTION OF THE FORMALDEHYDE ON THE ACCEPTOR COLLECTS IN THE LOWER PART OF THE COLUMN AND THE ALCOHOL BECOMES CONCENTRATED IN THE UPPER PART OF THE COLUMN, WITHDRAWING THE CONCENTRATED SOLUTION FROM THE SAID LOWER PART AND THE ALCOHOL IN VAPOR FORM FROM THE UPPER PART OF THE COLUMN, AND SUPPLYING TO THE SAID COLUMN ADDITIONAL AMOUNTS OF THE ACCEPTOR AS REQUIRED FOR ACCEPTING THE FORMALDEHYDE, THE ACCEPTOR BEING INTRODUCED AT A POSITION ABOVE THAT OF INTRODUCTION OF THE GASEOUS FORMALDEHYDE. 